Repression of Mitochondrial Citrate Synthase Genes by Aluminum Stress in Roots of and .

Aluminum (Al) toxicity in acid soils influences plant development and yield. Almost 50% of arable land is acidic. Plants have evolved a variety of tolerance mechanisms for Al. In response to the presence of Al, various species exudate citrate from their roots. Rye ( L.) secretes both citrate and malate, making it one of the most Al-tolerant cereal crops. However, no research has been done on the role of the mitochondrial () gene in Al-induced stress in the rye. We have isolated an gene, encoding a mitochondrial CS isozyme, in two cultivars (Al-tolerant cv. Ailés and Al-sensitive inbred rye line Riodeva; gene) and in two lines (Al-tolerant ABR8 line and Al-sensitive ABR1 line; gene). Both genes have 19 exons and 18 introns. The gene was located on the L rye chromosome arm. Phylogenetic studies using cDNA and protein sequences have shown that the gene and their ScCS protein are orthologous to genes and CS proteins of different Poaceae plants. Expression studies of the and genes show that the amount of their corresponding mRNAs in the roots is higher than that in the leaves and that the amounts of mRNAs in plants treated and not treated with Al were higher in the Al-tolerant lines than that in the Al-sensitive lines of both species. In addition, the levels of and mRNAs were reduced in response to Al (repressive behavior) in the roots of the tolerant and sensitive lines of and .